1. Field of the Invention
The present invention relates to methods for determining fuel flow and improving thermal efficiency for fossil-fired steam generator systems via thermodynamics and more particularly to a method for monitoring the operation of such a system by analyzing the dry fuel chemical composition, the effluent O.sub.2, and the principal composition of combustion effluents CO.sub.2 and H.sub.2 O. In addition, the instrument measures the concentrations of the common pollutants produced from fossil combustion. These pollutants include: CO, SO.sub.2, SO.sub.3, NO, NO.sub.2, N.sub.2 O, and hydrocarbons gases such as CH.sub.4. Having computed the fuel flow rate, and knowing the fuel's chemical composition, the plant's effluent flow rates can then be determined.
The importance of accurately determining thermal efficiency is critical to the thermal performance monitoring of any fossil-fired steam generator system. If practical day-to-day improvements in efficiency are to be made, and/or corrections to thermally degraded equipment are to be found and corrections taken, then accuracy in determining thermal efficiency is an obvious necessity. The art of tracking the efficiency of a conventional power plant or any fossil-fired steam generator plant lies fundamentally in measuring the useful output and the total energy flow of the input fuel.
While the art of measuring the useful output of such a system is highly developed, measuring the total energy flow of the input fuel has traditionally caused significant problems. Measurement of the useful output of a conventional fossil-fired steam generator system can be either the steam flow produced or the subsequent electrical power generated via, commonly, steam expansion in turbines. Measurement of the energy flow of the input fuel requires knowledge of the heating value of the fuel and its mass flow rate.
The importance of accurately determining pollutant concentrations and their effluent flow rates is also critical to the practical operation of any fossil-fired steam generator system due to environmental constraints imposed through regulatory operational limitations, the potential of regulatory induced fines and concern by the owner of the facility for environmental protection.
2. Description of the Prior Art
Present industrial technique for measuring fuel flow, given uncalibrated devices, results in minimum variances of .+-.1.6% for gas and oil fuel flow measurements; and typically a minimum .+-.3.0% variance for coal fuel flow measurement given its bulk nature. It is not uncommon for a coal-fired system to find fuel flow variances over .+-.10% on any given day. It should also be noted that typical variances associated with measuring the flow of compressed water can vary typically between 0.5% to 2.0%; however, with proper calibration the variance can be reduced to .+-.0.25%. The measurement of fuel flow, indeed the measurement of any flow, has traditionally been accomplished via measurement of its mechanical effects on a device. Such effects include the pressure drop across nozzles or orifice plates, unique fluid densities, unit weighing of fuel handling conveyor belts (commonly used for coal fuel), speed of sound, nuclear resonance, change in bulk storage liquid levels, etc. Such fuel flow devices require careful calibration to achieve acceptable accuracy (acceptable accuracy for fuel flow, on a daily basis, is assumed to be less than .+-.1.0%).
A related technique, in philosophy, to the present invention has been developed by the Electric Power Research Institute at the Morgantown power plant. This technique is termed the "Output/Loss" Method. Refer to the technical paper by E. Levy, N. Sarunac, H. G. Grim, R. Leyse and J. Lamont, "Output/Loss: A New Method for Measuring Unit Heat Rate", Am. Society of Mech. Engrs., 87-JPGC-Pwr-39. This method produces boiler efficiency independent of fuel flow, if heating value and the working fluid's energy flow is known, unit thermal efficiency can be determined. The technique relies on measuring emission gas flow directly. Knowing emission gas flow allows the determination of the majority of the thermal losses associated with combustion, called "stack losses". However, it is not practical for most coal-fired units for the following reasons: 1) it does not address measurement of flue gas concentrations as the present invention (thus no updating of heating value, as accomplished by this invention, heating values can vary considerably from different mines and in their moisture contents); 2) the errors in gas flow measurements in irregular ducts can exceed .+-.20 % resulting in .+-.2% error in boiler efficiency, and when combined with error in the working fluid's energy flow of at least .+-.1%, will result in at least .+-.3% error in unit efficiency; 3) the technique of direct flue gas flow measurements does not meet current U.S. Environmental Protection Agency's accuracy requirements of .+-.10%; and 4) the technique does not purport to determine emission flow rates since emission concentrations are not known through the technique which is an integral feature of the present invention.
In summary, inherent inaccuracies in direct fuel flow measurements which occur on a day-to-day basis for a gas or oil-fired plant, using present art with uncalibrated devices, are in the range of approximately 2% to 5%. For a coal-fired plant the variance in flow associated with direct measuring uncalibrated devices is typically 5% to 15% with a most likely variance of .+-.10%. With indirect fuel flow measurements using the Output/Loss Method, the variance in fuel flow is most likely no better than .+-.2%. It must be noted that for a coal-fired plant these ranges of accuracy are significantly wide to preclude trending of the monitored fuel flow rate for reasons of thermal efficiency or for detecting degraded equipment. However, at .+-.2% to .+-.10% variance the fuel flow rate is considered sufficiently accurate for gaseous emission flow determinations, but again, without knowledge of the effluent concentrations the individual effluent flow rates remain unknown.
Another important consideration is the variation in the fuel's heating value due to variations in fuel supplies and water content. Processes which address such variation in fuel heating value are discussed below.
The present invention solves the problems associated with measuring the energy flow of the input fuel whereby the fuel mass flow rate, the concentrations of common pollutants, the emission flow rates of the common pollutants, and the thermal efficiency of a fossil-fired steam generator system can be accurately determined.